When a sensor for sensing the revolution of an engine fails, a conventional engine controlling apparatus becomes inoperative and the engine cannot be started. However, there is an increasing trend to provide a minimum necessary operation of the engine even when part of the control system is out of order. Particularly in the case of a controlling apparatus equipped with an electronic distributor, a proposal has been made in Japanese Patent Laid-Open No. 58-2469 (1983) published on Jan. 8, 1983 in the title of "Engine ignition control circuit" to output a pseudo ignition signal when part of a revolution sensor is out of order.
However, the prior art technique explained above does not at all take backup means into consideration when the revolution sensor does not at all operate. Accordingly, with total failure of the sensor the engine cannot operate at all.